The present invention relates to a floating-caliper spot-type disc brake including a caliper which is axially slidably guided on a brake support member, the caliper having on one side of the brake disc a hydraulic brake-actuating device incorporating a mechanism for adjustment of the brake clearance between the brake disc and friction pads of the brake shoes.
Floating-caliper spot-type disc brakes embrace the brake disc in a U-shape. However, on only one side of the brake disc is the floating caliper equipped with a hydraulically movable brake-actuating device which axially displaces the brake pad on this side of the brake disc. The brake pad on the opposite side of the brake disc is moved indirectly by the floating caliper, which bears via the cylinder housing against the piston or directly against a second piston located in the cylinder housing. After the brake pad close to the piston has been applied to the disc, the reaction force will move the second brake pad until it abuts the disc by displacing the caliper and enables the braking action. Upon termination of the braking action, the required clearance will be adjusted on the piston side by the resetting of the piston, for instance, by means of an elastically deformed sealing ring.
Movement of the floating frame or fist-type caliper in its guides, predominantly on account of the blows exerted by the disc, will under normal conditions provide the adjustment of a brake clearance even for the brake pad close to the frame, or in other words, the outboard reaction, or indirectly actuated brake pad. However, if the guides for the caliper do not allow ease of movement, there occur known disadvantages, such as squeaking, grinding and uneven pad wear.
An adjustment of the clearance for the outboard brake pad or brake pad close to the frame of a floating-frame disc brake is known from German Patent DE-AS No. 2,258,116, which adjustment is accomplished mechanically by means of a holding and guiding spring arranged between brake support member and brake frame. A resetting movement of the frame and the brake pad abutting thereon is provided by the holding and guiding spring being supported on at least one sloped ramp of the brake support member inclined in the direction of the brake disc which produces a force component pointing axially to the disc, so that the frame will be moved in the direction axially away from the disc by the additional assistance of the spring effect created by the cross-leaf spring and of blows exerted by the disc. This contributes to achieve a clearance at the brake pad close to the frame.
However, there is the difficulty in these devices to correctly match the spring force and the angle of inclination. Though these two values are properly selected when the brake is new, there may occur considerable discrepancies as to the amount of force required for displacement of the floating caliper in the event of contamination and corrosion of the floating caliper guides as the brake is used. Under these circumstances, the resetting of the frame will no longer be guaranteed, and the above-referenced disadvantages will appear.